1. Field of the Invention
The instant invention relates to ignition analyzers which display signal information related to the operation of the ignition systems of multi-cylinder internal combustion engines, such as automobile engines, on an oscilloscope for use by a mechanic in analyzing engine performance.
2. Description of the Prior Art
Ignition analyzers utilizing oscilloscope displays are well known in the art and well accepted by both the professional and amateur mechanic as instruments for providing detailed information regarding the performance of a particular internal combustion engine, usually an automobile. The most basic display format utilizes electrical signals related to the voltage impressed across each spark plug of the internal combustion engine and displays these signals throughout one engine cycle, that is, through one cycle of firing of each spark plug. This is called the parade mode of display. Typically a magnetic or capacitive probe is connected to the secondary circuit of the ignition system at the high tension wire leading between the coil and distributor. The signal developed thereby is then suitably amplified and provided to the vertical input of an oscilloscope to drive the oscilloscopic trace vertially. The horizontal input of the oscilloscope is provided by a ramp generator which is synchronized with the engine cycle, that is, the ramp moves the oscilloscopic trace across the face of the display once per engine cycle. This is normally accomplished by synchronizing the beginning or end of the ramp to the firing of a particular cylinder, conveniently called cylinder No. 1. The major drawback to the parade mode of display is that the horizontal width of the oscilloscopes is in practice insufficient to show all the cylinders of a multi-cylinder engine in sufficient detail to provide all the required information.
In the stacked mode format of display, which was developed to overcome this drawback of the parade mode, the ramp moves the trace through its horizontal range of motion once per cylinder ignition. This is usually accomplished by synchronizing the beginning of the ramp to the spike of energy at the beginning of a cylinder's ignition time.
In order to avoid superimposing the traces related to each cylinder upon each other, the stacked mode provides a vertical separation between the traces related to the different cylinders. That is, cylinder No. 1 would be displayed across the bottom of the scope face and cylinder No. 2 and on displayed vertically above the lower traces.
The major drawback to the stacked mode of operation is in that the vertical dimension of the traces is limited by the number of cylinders required to be displayed at the same time. Although the horizontal information may be displayed more clearly than in parade, the vertical information is severely limited.
One solution to this problem is to provide two oscilloscopes, the first arranged to display the parade mode and the second to display a single cylinder firing in a manner similar to the stacked mode of operation. This is, of course, expensive and inconvenient.
Ignition analyzers also generally provide a power balance function by which the mechanic is provided with a mechanism for preventing ignition within a particular cylinder while monitoring engine performance changes. This is not necessarily associated with an oscilloscope display but may be provided in the same instrument. The power balance mode of operation requires that the individual cylinders be separately identifiable and this is conventionally accomplished by means of a counter. The counter is typically arranged to change value or count every time any spark plug fires and is then reset when the spark plug associated with cylinder No. 1 fires. A selector switch and comparator function is normally provided allowing the counter value associated with a particular cylinder to activate the ignition prevention device so as to disable the ignition system only at the proper time. Such ignition prevention devices are typically electronic shorting switches connected across the distributor points so that the points are rendered effectively inoperable where the switch is activated.